which tour to do?

I am planning to go snorkelling at Marietas Island on our trip in January. I have found three tours that go to this area and seem to allow at least a half day for snorkelling and kayaking. They are Ecotours, Vallarta Advenutre Tours and Princesa. Does anyone have any first hand knowledge of any of these? They are all priced about the same and all seem to offer a similar experience, but I am wondering if one company might be preferable. I have only snorkelled once so am not eperienced in this area. Your expert opinions would be welcome.

Definitely do the Geronimo to the Marietas. Best of all!